1. Field of the Invention
The invention relates to processing of materials. More particularly, the invention relates to selectively destroying a portion of a material by using focused optical radiation and ultrasound waves.
2. Background of the Related Art
Both ultrasound and photodisruptive lasers have been used for material processing and tissue destruction. For example, ultrasound-driven phacoemulsification of the lens is a common surgical intervention in the eye, while Nd:YAG laser photodistruption of secondary cataracts is a common medical laser procedure. Destruction of a medium or tissue with ultrasound can be produced with sufficiently high powers such that absorption of the field heats the material directly and thereby destroys it. Alternatively, an inhomogeneity such as an inclusion, gas bubble or void can strongly couple to the ultrasound field, thereby mechanically destroying material in the vicinity of the inhomogeneity. In aqueous media, cavitation bubbles are commonly used to produce this effect. Finally, destruction of materials can be accomplished by direct mechanical vibrations, in which ultrasonic energy is transferred through a probe in a xe2x80x9cjackhammerxe2x80x9d fashion.
Phacoemulsification is a procedure that uses both cavitation and direct mechanical vibration in the lens of the eye by means of a probe, which also directs an acoustic field to drive these nuclei and produce a strong mechanical effect. This leads to emulsification of the lens material, which is subsequently aspirated and removed. In many materials, and especially tissues, cavitation nuclei are not normally present. In these cases, ultrasonic destruction of material must occur by the invasive introduction of nuclei, by direct ultrasonic absorption or by direct mechanical vibrations coupled into the material with a probe.
Various uses of lasers or ultrasound for destroying tissue are known in the art. For example, U.S. Pat. No. 4,960,108 discloses a method in which pulsed laser radiation situated in the infrared region is concentrated by means of an optical waveguide at a concrement to be destroyed which is surrounded with aqueous rinsing liquid. The concrement is destroyed mechanically by laser-induced breakdown of the rinsing liquid, giving rise to shock wave and cavitation. Ultrasound is not used in this method.
U.S. Pat. No. 5,582,578 discloses a method utilizing two shockwave pulses with a specified time delay and pressure relationship, the first shockwave pulse being used to induce a transient cavitation bubble cluster near the target concretion, and the second shockwave pulse to control and force the collapse of the cavitation bubble cluster towards the target concretion with concentrated energy desposition. The method does not involve the use of a laser. U.S. Pat. No. 5,800,365 shows a similar method.
Another method using only ultrasound is disclosed in U.S. Pat. No. 5,676,692. This method involves placing a reflector of ultrasound or an ultrasound energy conversion device which converts received ultrasound energy to heat adjacent the tissue to be treated. The use of lasers is not disclosed in the method.
A method involving the use of multiple ultrasound transducers is disclosed in U.S. Pat. No. 5,725,482. This method uses a plurality of standing compression waves established within the medium along corresponding longitudinal axes between opposing pairs of coordinated transducers. The target volume is located at the common intersection of the axes of the standing compression waves. This method does not involve the use of lasers.
U.S. Pat. No. 5,219,401 discloses an apparatus for selective destruction of cells by implosion of gas bubbles. The gas bubbles are created by cavitation provoked by an ultrasonic wave generator. Implosion of the gas bubbles results in destruction of cells situated adjacent to the imploded gas bubbles. The apparatus does not disclose creating a cavitation nucleus by focusing optical radiation.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.
Conventional systems and methods, including those discussed above, have various problems and drawbacks. For example, it can be difficult to precisely control the area of destruction with the known systems and methods. The present invention, among other things, remedies this problem.
The present invention includes a method of materials processing that includes the creation of a cavitation nucleus in a first portion of the material, or adjacent to the material, by focusing optical radiation at approximately the first portion of the material, or adjacent to the material, and causing mechanical disruption in a second portion of the material adjacent to the cavitation nucleus by subjecting the cavitation nucleus to ultrasound waves.
In particular embodiments of the invention, the optical radiation creates the cavitation nucleus by causing optical breakdown of the first portion of the material. In some of these embodiments, the optical radiation is sufficiently focused so that optical breakdown of substantially only the first portion of the material occurs.
In some embodiments, the optical breakdown results in the ionization of the first portion of the material.
In some embodiments, the optical radiation is a short pulse duration laser beam. In some of these embodiments, the pulse duration of the laser beam is between about 1 femtosecond and about 1 nanosecond.
In some embodiments, the frequency of the ultrasound waves is determined based on a size of the cavitation nucleus.
In some embodiments, the wavelength of the optical radiation is such that the material is transparent to the optical radiation.
In some embodiments, the laser beam has a wavelength of between about 400 nm and about 2xcexc.
In some embodiments, the optical radiation is directed to the first portion of the material by a fiber optic probe. In some of these embodiments, a sighting device is used to direct the fiber optic probe.
In some embodiments, the ultrasound waves are focused at or proximate the cavitation nucleus.
In some embodiments, the ultrasound waves cause a mechanical disruption in at most the first and second portions of the material.
In some embodiments, the second portion of the material is biological material and is destroyed, and a third portion of the material is not destroyed, the third portion of the material being that portion of the material other than the first and second portions of the material.
In some embodiments, protein is introduced into the material, the protein stabilizing the cavitation nucleus by surrounding the cavitation nucleus. Stabilization can also be achieved with lipids. The lipids may be introduced or already present in a particular material.
Particular embodiments of the invention include an apparatus for processing a material in accordance with the methods discussed above.
Some embodiments of the invention comprise a platform to which the optical radiation generator and the ultrasound transducer are mounted, wherein the material is a body of water and the apparatus is for producing a cavitation signature in the body of water.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. Objects and advantages of the invention may be realized and attained, in part, as particularly pointed out in the appended claims.